The xerographic photocopying process has been extensively described and is well understood. Typically, a photoconductive material is mounted on a drum or on an endless belt to hold a latent electrostatic charge image prior to development and transfer to a plain paper copy.
In one type of photocopy machine a photoconductor drum is employed. While the drum is rotated it is exposed to a line image of an object by the relative movement between a slit and an illuminated object. In another type of photocopy machine the drum is replaced with a photoconductor belt which may be endless for continuous motion along a belt path. The belt path is defined by a plurality of roller elements which are spaced to provide a belt path section where the belt is flat while being exposed to a planar image of the object instead of through a moving line image.
The flat photoconductor belt section may be flash exposed. When the light intensity of the flash is sufficiently high, the exposure time may be so short that blurring of the latent image on a continuously moving photoconductor belt is prevented. The short flash exposure of the entire object enables a high speed photocopying operation.
Various materials have been proposed for photoconductors in photocopy machines. One well-known material is made of a selenium material which is capable of producing a substantial number of copies before replacement. Another material may be of the organic type such as described in the patent to Shattuck et al U.S. Pat. No. 3,484,237. However, an organic photoconductor material has a limited useful life and thus requires replacement in a manner such as, for example, taught and shown in the patent to Berlier et al U.S. Pat. No. 3,588,242.
In the Berlier patent a copy drum is described utilizing an organic photoconductor stored as a flexible strip on a supply reel located within the interior of the drum. The photoconductor is fed around the external periphery of the drum and returned to a take-up reel located inside the drum. The entire photoconductor strip used on the drum is periodically automatically replaced with a fresh unused photoconductor on the supply reel after a certain preselected number of copies have been made.
Another approach for replacing a photoconductor belt is described in the patent to Swanke U.S. Pat. No. 3,619,050. In this patent a photoconductor web is stored in a cartridge located near a photoconductor belt path. A photoconductor segment is formed into an endless belt by use of a connecting tow bar and wrapped around appropriate roller elements which define the photoconductor belt path necessary for exposure, transfer and development of the copy. A replacement of the used web is carried out by taking selected segments from the nearby available cartridge supply and feeding this around the rollers and then reconnecting the ends at the two bars to form an endless belt. A complex mechanism for replacement of the photoconductor is described involving substantial manual control.
In the German patent publication 2,309,296, published on Sept. 6, 1973, based upon an application date of Feb. 24, 1973, a photoconductor is formed into an endless loop. The loop forms a removable cassette having a supply roll and a take-up roll. The loop is passed around rollers and a copy platform around which an exposure area and a printing stage are closely grouped. The casette moves back and forth along a straight path during the copying process.
The desirability of using a flash exposure of a flat photoconductor segment may be appreciated. The moving slit mechanism to expose a drum-type photocopier with a line segment is deleted and a relatively convenient and economical optical exposure system can be used. This advantage of the belt photocopier may be appreciated from the large number of belt photocopiers described in the art such as in the patents to Gardner et al U.S. Pat. No. 3,521,950 Hewes et al U.S. Pat. No. 3,661,452 and Swanke U.S. Pat. No. 3,619,050.
Although the photoconductor drum structure disclosed in the Berlier patent effectively provides a long life by virtue of the storage of a replacement section within the drum, the Berlier apparatus still operates with a line segment exposure by virtue of its drum mounting and does not lean itself to the photoconductor belt photocopy machine.
Another disadvantage of the Berlier replacement structure involves the photoconductor belt replacement operation. This is carried out after a preselected number of copies have been made. At such time the entire photocopying process is interrupted until the cycle for replacement of the photoconductor segment extending around the entire drum is completed.
The patent to Begun et al U.S. Pat. No. 2,789,776 discloses an apparatus manually positioning successive lengths of a recording medium on an endless recording track such as on the periphery of a rotating drum. Ratchet wheels are employed to pull successive lengths of the recording medium around the periphery of the drum to expose new lengths for recording or playback.
Although in a photocopy machine one could employ a longer copying life selenium type photoconductor, its cost and manufacturing complexities reduce the desirability for such approach; particularly when the selenium photoconductor in the belt form has a significantly less useful lifetime then selenium in the drum shape.
When an organic photoconductor is employed in a belt form such as shown in the apparatus disclosed in the patent to Swanke, then an undesirable frequent replacement operation must be carried out even though the organic photoconductor is retained in a nearby cartridge.